Scroll-type fluid displacement apparatus, such as compressors, vacuum pumps, air motors, expanders, and the like are often used in equipment such as air brakes, air conditioners and refrigerators, for example, and are favored for such applications because they tend to be quieter in operation than reciprocating fluid displacement apparatus. Scroll compressors, in particular, normally include at least one fixed and one orbiting scroll member. Each scroll member has a scroll blade, involute or wrap meshed with the other's scroll blade to define suction areas or zones at the outer edges of the scroll members, fluid voids between the scroll members, and an outlet at the center of the scroll members.
Eccentric crank mechanisms are normally used to maintain the scroll members in a specific orbiting relationship with respect to one another. The crank mechanisms include a shaft rotatably mounted to a housing of the compressor, and an eccentric portion fixed to the shaft. As is known, the eccentric portion has an axis offset from an axis of the shaft. The orbiting scroll member is operatively connected to the crank mechanism through the eccentric portion, such that the orbiting scroll member will orbit, but not rotate with respect to the fixed scroll member, as the shaft and eccentric portion of the crank mechanism rotate.
Such eccentric crank mechanisms are shown, for example, in U.S. Pat. No. 4,192,152 to Armstrong et al. and U.S. Pat. No. 5,154,592 to Ohtani et al. A separate driveshaft is operatively connected to the orbiting scroll member and is turned by a motor to orbit the orbiting scroll member on the crank mechanisms, and about the fixed scroll member. As the orbiting scroll member orbits, the fluid voids between the scroll members become smaller towards the center of the scroll members and compress the fluid contained therein. The compressed fluid is then expelled under pressure from the outlet at the center of the scroll members.
In order to reduce the number of parts and complexity of a compressor, parts are preferably combined whenever possible. U.S. Pat. No. 5,165,878 to Inagaki et al. and U.S. Pat. No. 5,556,269 to Suzuki et al., for example, each disclose a scroll compressor including an eccentric crank mechanism having a shaft extending to a motor. In effect, therefore, the eccentric crank mechanism is combined with the driveshaft, such that the total number of parts and complexity of the compressor is reduced. Suzuki et al. also discloses an auxiliary driveshaft that is driven by the "main" driveshaft with a timing belt. Multiple driveshafts are sometimes preferable to more evenly distribute stresses within the compressor, and/or improve the efficiency of the compressor. Neither Inagaki et al. nor Suzuki et al., however, disclose or suggest means for harnessing excess power of the driveshaft for auxiliary machinery, such as a fan or another compressor stage for example.
Preferably, therefore, means are also provided for harnessing excess power of the compressor. U.S. Pat. No. 5,466,134 to Shaffer et al., for example, discloses a scroll compressor having a driveshaft and a separate, eccentric crank mechanism that is externally accessible so that the rotational motion of the eccentric crank mechanism may be harnessed to drive an auxiliary machine. A drawback of this design, however, is that the excess power isn't taken directly from the driveshaft but is transferred through the eccentric crank mechanism, which may result in an inefficient transfer of excess power to the auxiliary machine, and additionally stresses during operation of the compressor. These additional stresses may in turn require inefficient and expensive overbuilding of the crank mechanism, which may in-turn increase the temperature of, or hinder the cooling of the compressor during operation.
What is still needed and desired is a scroll-type fluid displacement apparatus having fewer parts, yet wherein excess power is accessible directly from the drive shaft. Also, the fluid displacement apparatus will desirably include multiple drive or input shafts so that stresses will be more evenly distributed within the apparatus. Furthermore, any eccentric crank mechanisms or drive shafts should be mounted or designed to provide adequate room for the use of strengthening and heat dissipating ribs.